Antenna system problem solving

[bep]

This post is going to cover a lot of sub forum areas. Should I be in the wrong place please advise, and sorry.

Trying to listen to Overlay Regional InterOperability Network (ORION) Trunking System, Various, Virginia - Scanner Frequencies Site 2 only.
Scantenna on roof two stores up.
At sea level. 23451 zip code
Approx. 75-100 feet of unknown type coax preinstalled by audio/video company 13 years ago.
Amplifier at antenna and one at scanner
Pro 197
All other systems in my area come in great

Now that you have all the info I am not sure what to do next in trying to determine why I cannot receive this system. Up until a month ago the system came in marginally. Now I have 5 bars in strength, but the "T" hardly ever shows. Listening to the stream the system sound poor also, but receiving more than I. Without the two amplifiers I receive zero bars. Getting to the roof is an issue unfortunately, since I cannot find anyone to assist me.

My next idea is to go to the attic where the coax connection is and throw a new coax over the roof and connect through a window as a test.

Again if someone could suggest me trying idea A then idea B I can solve this quickly as possible.

Frustration is high

Thanks

 

[rbm]

Is that antenna and coax EXACTLY what you were using to receive that system before the problem started?

I've found the 'Scantenna' not to be the best for that band.
Also, among my 5 ST2 antennas, I've seen some variability on that band.
That may be caused by variations in the balun or mechanical connections of the elements.

Another big hitter is that the ST2 is directional. Especially on the higher frequencies.

What is the type and gain of each of the amplifiers?

The first thing I would try is remove the amplifier at the scanner to see if you get any improvement.

Also:
Assuming that you're using 'F-Type' connectors in your feedline, you could add a splitter to add as an attenuator to see if that improves anything.

'Ball park' losses for splitters:
A 2-way splitter has around 4 dB loss
A 3-way splitter has around 7-8 dB loss
A 4-way splitter has around 9-11 dB loss
Those numbers vary widely depending on manufacturer so you have to check the specs.

You could be overloading the scanner.
BUT ...
You could also be overloading the amplifier at the antenna.

Are all of the other systems that you're receiving well in the 700/800 MHz band also?

In addition:
Your coax could be loosing too much signal in that range ....
OR
Your amplifier isn't performing well in that range.

This is where a USB dongle would come in handy so you could 'visualize' what's happening.

Rich

 

[rbm]

For comparison purposes, here's how the ST2 compares against a 'real' antenna on the 800 MHz band.

On the left is an ST2 and on the right is an Antenex (Laird) FG9026.
Both of them have LNA-1000 amplifiers right at the antenna.

They look similar, BUT the ST2 is running with almost 28 dB more RF gain.
That's a big difference.
The ST2 won't even hear weaker signals while the Antenex can receive them full quieting.

Rich

 

[bep]

Thanks RBM,
A lot to consider.
Nothing has changed in the setup since loss of signal. It comes to mind that the signal, when working, was lost when it rained for some reason.
Virginia Beach also has an old 800 (non digital) system that I can hear loud and clear. Good idea to check.
Many things to check, and cannot get to them until the first of the week. Currently SO has my attention all weekend.
Will report back as soon as I can.
Thanks
Bruce

 

[popnokick]

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There have been multiple reports here on RR of signal multipath problems with the ORION system in / near VA Beach. Go to the Virginia Discussion Forum and search using "Orion" as your keyword.

 

[bep]

Ok, stupid me actually got smart.
I brought in my Pro 96 that was programmed the same as the 197. Connected to the amplified splitter and have them sitting side by side. The 96 is doing 75% better on receiving a signal (still not great) while the 197 just keeps scanning. The "T" is displayed way more on the 96 than the 197. I switched coax lines from the splitter and no change.
Using Win500 i checked the settings on both units and they are the same.
Possibly I am looking at a bad unit???

 

[bep]

Now to get caught up. Today I was able to play a little in trying to determine whats what. I bypassed the power amp/splitter at the radios. This seems to actually be better. However I still do not understand that I definitely needed it months ago. However it is better and the "T" is visible much more than before. I am still splitting the antenna by 4. I still get dropped conversations. I do see the signal bars go from 5 bars to nothing then spring back to 5 bars.
Any suggestions on where to go from here?

Thanks

bruce

 

[Jim41]

Some thoughts

Now to get caught up. Today I was able to play a little in trying to determine whats what. I bypassed the power amp/splitter at the radios. This seems to actually be better. However I still do not understand that I definitely needed it months ago. However it is better and the "T" is visible much more than before. I am still splitting the antenna by 4. I still get dropped conversations. I do see the signal bars go from 5 bars to nothing then spring back to 5 bars.
Any suggestions on where to go from here?

Thanks

bruce

My thoughts:
1. While scanning the ORION system using your Pro 197 (during a period of no voice traffic) press FUNC and then TUNE. Verify the display shows a valid control channel frequency. Then monitor the control channel successful decode % over several minutes. If the numbers are low (less than 80%) or vary wildly, it is an indicator of reception problems.

2. I live in Hampton. When I do this with ORION site 1, I get 4 bars of signal strength, a fairly steady "T", but successful decode % of 0% to 20%. I am using a PSR-600. I assume this performance is due to simulcast distortion.

3. I have not tried using a directional antenna.

4. I have this system programmed with Multi-site mode = Off and cc dwell time = 200.

Jim41

 

[bep]

Following your directions for Tune the display is as follows:
P25 and the CC frequency or sometimes au and the CC frequency
--% N:--- W:--- but sometimes displays --% N:1E0 W: BEE00

Not sure what I am looking at here.

 

[Jim41]

Following your directions for Tune the display is as follows:
P25 and the CC frequency or sometimes au and the CC frequency
--% N:--- W:--- but sometimes displays --% N:1E0 W: BEE00

Not sure what I am looking at here.

If you are successfully decoding the control channel, there should be a number from 1 to 99 to the left of the % sign. The number indicates the percent of control channel samples that are successfully decoded. You need a high % number to successfully listen to a trunked system. A low % number can be an indication of the infamous simulcast reception/decoding problems.

Try this on other trunked systems you can receive and compare the % numbers with ORION site 1. Put the unit in your car and try other locations in VB.

The only solution to the simulcast problem I know of that has worked for some others is to install an outside directional antenna.

Jim41